Building the Echo Base PCB

[Granny Gremlin]

Resocketting the TL072 in the modulation section fixed the LED (no longer turns off at one extreme of the shape pot's travel and appears to flash the modulation rate when modulation is on, solid when off; a nice touch I was not expecting).  That got my hopes up, but the modulation itself is not working yet.  The delay itself is nice, but wish it had more repeats before oscillation.  Hopefully that's related to the modulation problem. 

I haven't tried outright  replacing that op amp yet (resocketting improved things), but wondering if anyone else has any ideas about what could be wrong?

[Taylor]

OK, so if your LED is flashing, then the LFO is oscillating. Since it isn't modulating the delay time, the issue lies in the linkage between the LFO and the delay chip. Check your BC560 transistor and the resistors around it, as well as the LFO Depth pot for any issues/bad solder joints.

I'm not sure I understand what you mean about having more repeats before oscillation. The point of oscillation is when feedback = >100%. 100% exactly would be infinite repeats. Perhaps what you're saying is that your feedback reaches the point of oscillation too soon in the feedback pot's throw, like if it starts oscillating with the knob at center and is just all oscillation above that point. You can decrease the maximum feedback level (and thus spread the useful range of the pot out further) by increasing the value of the 20k resistor right below the feedback pot.

[Granny Gremlin]

Thanks for the tips; I'll check around the 560.  Quite sure I checked the Depth pot connections but it bears checking again.

Oscillation doesn't start as early as your example; somewhere between 1/8 and 1/4 turn before max which is reasonable in terms of the pot travel (I suspect this would vary with delay time setting, but didn't check).  I wouldn't think there's much to be done about this for the reasons you mentioned, I just wish it 9x% feedback was equal to a higher number of repeats... (near)-infinate repeats isn't feasible being more looper territory, or some middle ground between, which is what I've been longing for; didn't mean for that to sound like a complaint (it's not significantly different in this regard to any other delay I have used, or at least the analog ones).  Once I get everything else working I'll see how I feel about it and consider the resistor change you mentioned; thanks for that tip too.  I doubt I'll bother with it though, but we'll see.

Once I'm done with this (and the second one waiting in line behind it for the offboard wiring to be connected - one for me and one for a bud) I have a Meat Sphere I am itching to try out.  Cheers.

[Granny Gremlin]

Removing the 560 (no surprise but could get a good read on it in circuit) I buggerred the base lead so I tested a fresh one and replaced it.  Still no modulation.  I looked at pics of other people's completed/working boards and I got it in the right way round. 

The pots, including Depth, are good.  The 220R in series with base is good.  The 240K on the other side of Depth (on the shape pot) is good; can't get a read on the 39K across emitter and collector in circuit so reflowed but no help either.

Now the embarassing bit starts.  I checked the 10u cap between Depth and the 240K and couldn't get a good read.  Looked at the label: 2.2u BP.  I have no idea how that happenned other than I was trying different cap types on the 2 boards I have going (just to see what diff it could make - never built 2 of the same at the same time) and my hand must have strayed.  Replaced that with a 10u tant but still no good. 

Just staring at the board in despair and I notice the 2 resistors under the 560 have the same stripes.  Sheeeeeeeeeeeeet. Checked my "39K" bin and sure enough it's full of 220Rs and 1 last 39K.  Put that one in and we have modulation!  Man that can do some weird stuff; going to enjoy that after I stop feeling like such a bloody dufus.

Thanks so much for the help.

[Taylor]

Nice! Happy to help. That feeling of something springing to life is a good one.

[Granny Gremlin]

Both boards wired up and working.  Enclosure paint by the GF of the guy the second one is for.





Haven't A/Bed properly yet (will have my friend do it blind) but from testing them both my initial impression is that there is little tonal advantage to using tropical fish over modern generic box films (but there is a disadvantage - nobody makes PCBs which leave enough space for tropical fish - I had to mount 2 caps, one fish and one electro, on the underside of the board to fit it all in).

[naught101]

Hey Taylor,
I've just finished building your board, and I'm getting no sound out of the guitar, just a lot of noise. I posted all of the troubleshooting guide details, as well as answers to a few questions over at http://www.diystompboxes.com/smfforum/index.php?topic=112193.0 - let me know if it's better to re-post them here.

[WorthTheWords]

Hey Taylor- I'm a pretty new builder, and a first time poster.

I've finished the echo base, but am getting no echos. I get the clean signal coming through fine, but no echos. Everything else seems to be working properly- if i turn the effect volume all the way up I get some noise that seems to be modulating properly with the LFO pots, including the waveshape mod. The LED lights up blinks as it should and clean kill switch is working. I'm also using the dub madness mod, but don't notice a change in the noise when that is switched on or off. Any suggestions on how to get the echos working?

I haven't used an audio probe, but will try figuring that out tomorrow.

Thanks for your help!

Joel

[WorthTheWords]

Good news. I was using an audio probe to test the IC pins, and right when I was just about done- out of nowhere everything started working! The whole circuit is now working as it should, and it sounds great!

Does this just sound like a finicky solder joint somewhere in the delay loop of the circuit?
Thanks again,

Joel

[slacker]

Good to see you got it working. Yes it could be a dodgy solder joint somewhere round the PT2399, maybe have a close look and touch up anything that looks suspect. Or it could just have been a bit of stray solder or scrap of wire shorting something out and your poking around removed it or if you've used  sockets maybe the chip wasn't seated properly.

[WorthTheWords]

Thanks slacker! I've really been looking forward to this build- and it hasn't disappointed. It sounds great! (When it's working). Unfortunately, the echos have stopped working again. I'll have to to a closer look at all the joints around the 2399. Thanks again!

[Taylor]

Sorry for my late reply - I moved to a different city this last week and haven't had internet access.

In addition to slacker's advice, since you're getting the modulated noise and the clean signal, it seems to me that the short/cold solder joint must be in between the input gain stage and the input of the delay chip. If it was the feedback loop, then you'd get one repeat and then nothing.

Also, when things spring to life when you move them: early on in my DIY'ing, I often had issues with wires, specifically right where they connected to the board. I didn't have a good wire stripper back then, and I was nicking the wires so much in stripping the ends that they were breaking when I'd flip the board around in debugging. Just something to notice in case it applies here.

[Sanguinicus]

Finally getting around to posting for some help, been sitting on this for a few months. I built the MusicPCB Echo Base. An excellent, high quality PCB. I've added the clean kill mod and the wave shape mod.

The issue I have is it's very noisy and distorted. Some of the guitar signal goes through but it's very faint and it's mostly a distorted noisy mess. All the knobs and switches work in that I get the desired function out of them. Level changes the volume, feedback changes the number of repeats, etc. Except they sound awful. I've posted a link to the file in Dropbox, I would appreciate if someone checked it out. I did also try the diode lift mod that some have suggested in other threads, but it made no difference. I've also tried 4 different PT2399 chips.

This isn't my first rodeo, I'm a pretty good solderer (I reflowed all the joints) and electronics sort of guy, so if there's anything I can specifically look for, that would be awesome. Component values are correct too, I went through and rechecked everything and had to replace one component. The file is a few sting picks and mucking around with the feedback and time knobs, you'll get the idea when you hear it.

I've made a kick arse box for this with a slide on decal and everything. I really want to get this working! I'll post some photos and Inkscape SVG file when I get it working.

Here's the link: https://www.dropbox.com/s/i5tchcd46oo1vim/Voice0001.mp3?dl=0

[slacker]

Is the dry signal clean or is that distorted as well? Sounds like everything is distorted in your sound clip, which would point to a problem around the first opamp.

[Sanguinicus]

Is the dry signal clean or is that distorted as well? Sounds like everything is distorted in your sound clip, which would point to a problem around the first opamp.

The dry signal goes through clean. I recorded the clip with my phone, so it's not the best. Take my word for it though, it is clean. Said another way, the dry signal sounds the same when the effect is on or in bypass. Everything works, all the knobs and switches do what they're supposed to do. Just that the repeats are very distorted.

[Taylor]

The PT2399 doesn't have a huge amount of headroom. What kind of pickups(/preamp?) does your guitar have? Did you have any other pedals in front of the Echo Base?

[Sanguinicus]

The PT2399 doesn't have a huge amount of headroom. What kind of pickups(/preamp?) does your guitar have? Did you have any other pedals in front of the Echo Base?

No other pedals infront. I tried three different guitars. All had the same effect. One was active pickups, then I went to a guitar with a JB and '59 in it, then a guitar with Dimarzios. All pickups showed the same problem, even winding down the volume on the guitar gave me the same thing. In my audio sample, if you listen carefully, you can hear clean repeats but they're hard to hear under all the noise.

Also running off a 9V power supply. Also tried with batteries. Nothing has worked so far.

Another issue I have is when the LFO is on, I hear the click of it. Let's put that to the side for now and get a good delayed signal going.

[garcho]

Another issue I have is when the LFO is on, I hear the click of it. Let's put that to the side for now and get a good delayed signal going.

could be related. when built correctly, there's no tick, and while there is distortion you can hear with basically any PT2399 build, it's not at all like what you recorded. sounds like you should take some voltages and post them.

[Sanguinicus]

Another issue I have is when the LFO is on, I hear the click of it. Let's put that to the side for now and get a good delayed signal going.

could be related. when built correctly, there's no tick, and while there is distortion you can hear with basically any PT2399 build, it's not at all like what you recorded. sounds like you should take some voltages and post them.

I can do that. Is there a diagram on here with what voltages should be and I can cross reference that?

I did measure voltages voltages a while back, and it seemed to check out. But I could be wrong.

I might measure out all the pins on the ICs and anything else important and post them up here when I get home from work.

[Sanguinicus]

So I measured voltages. I realised I haven't tried the mod that replaces the two 47k's with 22k's. Because the board is such high quality, it's a pain to remove components. So I'll solder another 47k on the underside of the board in parallel at the two locations to test.

Thing is though, if this mod worked, shouldn't it have worked anyway with the volume on the guitar turned down? I've even got a guitar with coil taps and in single coil mode, no dice. In any case, I'll report back. If it doesn't work, I'll post my voltages.

EDIT: so the resistor substitution didn't work. In fact, I had to hit the string harder to get anything out of it. I don't think it's because I paralleled resistors. See next post for those pesky voltages.